1. Field of the Invention
The present invention relates generally to wellbore valves, and specifically to tandem safety valves for use in a producing oil and gas wellbores.
2. Description of the Prior Art
Safety valves are provided in producing oil and gas wellbores to control the flow of production fluids, and are especially important in shutting-in the flow from the oil and gas well in the event a loss of control occurs. All prudent operators of oil and gas wells require a functioning safety valve in wells to ensure the safety of personnel, as well as to protect the economic value of the well. When a safety valve no longer operates properly, it must be replaced, typically by using a workover rig to pull the production tubing to allow replacement, but in subsea wells, pulling production tubing is so costly that instead an expensive wireline operation is usually performed to place a safety valve within the central bore of the production tubing.
It is advantageous, therefore, to provide a tandem safety valve having a valve in a mechanism wherein one of the tandem valves may be normally selectively opened and closed through selective application of fluid pressure to a valve actuator, and wherein the other of the tandem valves may be selectively locked into an open position without maintenance of hydraulic actuation pressure on the locking actuator.